/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 *
 *
 *
 *
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent.locks;

import java.util.*;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.*;

import vjava.util.concurrent.*;

/**
 * A reentrant mutual exclusion {@link Lock} with the same basic behavior and
 * semantics as the implicit monitor lock accessed using {@code synchronized}
 * methods and statements, but with extended capabilities.
 *
 * <p>
 * A {@code ReentrantLock} is <em>owned</em> by the thread last successfully
 * locking, but not yet unlocking it. A thread invoking {@code lock} will
 * return, successfully acquiring the lock, when the lock is not owned by
 * another thread. The method will return immediately if the current thread
 * already owns the lock. This can be checked using methods
 * {@link #isHeldByCurrentThread}, and {@link #getHoldCount}.
 *
 * <p>
 * The constructor for this class accepts an optional <em>fairness</em>
 * parameter. When set {@code true}, under contention, locks favor granting
 * access to the longest-waiting thread. Otherwise this lock does not guarantee
 * any particular access order. Programs using fair locks accessed by many
 * threads may display lower overall throughput (i.e., are slower; often much
 * slower) than those using the default setting, but have smaller variances in
 * times to obtain locks and guarantee lack of starvation. Note however, that
 * fairness of locks does not guarantee fairness of thread scheduling. Thus, one
 * of many threads using a fair lock may obtain it multiple times in succession
 * while other active threads are not progressing and not currently holding the
 * lock. Also note that the untimed {@link #tryLock() tryLock} method does not
 * honor the fairness setting. It will succeed if the lock is available even if
 * other threads are waiting.
 *
 * <p>
 * It is recommended practice to <em>always</em> immediately follow a call to
 * {@code lock} with a {@code try} block, most typically in a before/after
 * construction such as:
 *
 * <pre>
 * class X {
 * 	private final ReentrantLock lock = new ReentrantLock();
 * 
 * 	// ...
 * 
 * 	public void m() {
 *     lock.lock();  // block until condition holds
 *     try {
 *       // ... method body
 *     } finally {
 *       lock.unlock()
 *     }
 *   }
 * }
 * </pre>
 *
 * <p>
 * In addition to implementing the {@link Lock} interface, this class defines
 * methods {@code isLocked} and {@code getLockQueueLength}, as well as some
 * associated {@code protected} access methods that may be useful for
 * instrumentation and monitoring.
 *
 * <p>
 * Serialization of this class behaves in the same way as built-in locks: a
 * deserialized lock is in the unlocked state, regardless of its state when
 * serialized.
 *
 * <p>
 * This lock supports a maximum of 2147483647 recursive locks by the same
 * thread. Attempts to exceed this limit result in {@link Error} throws from
 * locking methods.
 *
 * @since 1.5
 * @author Doug Lea
 */
public class ReentrantLock implements Lock, java.io.Serializable {
	private static final long serialVersionUID = 7373984872572414699L;
	/** Synchronizer providing all implementation mechanics */
	private final Sync sync;

	/**
	 * Base of synchronization control for this lock. Subclassed into fair and
	 * nonfair versions below. Uses AQS state to represent the number of holds
	 * on the lock.
	 */
	abstract static class Sync extends AbstractQueuedSynchronizer {
		private static final long serialVersionUID = -5179523762034025860L;

		/**
		 * Performs {@link Lock#lock}. The main reason for subclassing is to
		 * allow fast path for nonfair version.
		 */
		abstract void lock();

		/**
		 * Performs non-fair tryLock. tryAcquire is implemented in subclasses,
		 * but both need nonfair try for trylock method.
		 */
		final boolean nonfairTryAcquire(int acquires) {
			final Thread current = Thread.currentThread();
			int c = getState();
			if (c == 0) {
				if (compareAndSetState(0, acquires)) {
					setExclusiveOwnerThread(current);
					return true;
				}
			} else if (current == getExclusiveOwnerThread()) {
				int nextc = c + acquires;
				if (nextc < 0) // overflow
					throw new Error("Maximum lock count exceeded");
				setState(nextc);
				return true;
			}
			return false;
		}

		protected final boolean tryRelease(int releases) {
			int c = getState() - releases;//减1
			if (Thread.currentThread() != getExclusiveOwnerThread())
				throw new IllegalMonitorStateException();
			boolean free = false;
			if (c == 0) {
				free = true;
				setExclusiveOwnerThread(null);
			}
			setState(c);
			return free;
		}

		protected final boolean isHeldExclusively() {
			// While we must in general read state before owner,
			// we don't need to do so to check if current thread is owner
			return getExclusiveOwnerThread() == Thread.currentThread();
		}

		final ConditionObject newCondition() {
			return new ConditionObject();
		}

		// Methods relayed from outer class

		final Thread getOwner() {
			return getState() == 0 ? null : getExclusiveOwnerThread();
		}

		final int getHoldCount() {
			return isHeldExclusively() ? getState() : 0;
		}

		final boolean isLocked() {
			return getState() != 0;
		}

		/**
		 * Reconstitutes this lock instance from a stream.
		 * 
		 * @param s
		 *            the stream
		 */
		private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
			s.defaultReadObject();
			setState(0); // reset to unlocked state
		}
	}

	/**
	 * Sync object for non-fair locks
	 */
	static final class NonfairSync extends Sync {
		private static final long serialVersionUID = 7316153563782823691L;

		/**
		 * Performs lock. Try immediate barge, backing up to normal acquire on
		 * failure.
		 */
		final void lock() {
			if (compareAndSetState(0, 1))
				setExclusiveOwnerThread(Thread.currentThread());
			else
				acquire(1);
		}

		protected final boolean tryAcquire(int acquires) {
			return nonfairTryAcquire(acquires);
		}
	}

	/**
	 * Sync object for fair locks
	 */
	static final class FairSync extends Sync {
		private static final long serialVersionUID = -3000897897090466540L;

		final void lock() {
			acquire(1);
		}

		/**
		 * Fair version of tryAcquire. Don't grant access unless recursive call
		 * or no waiters or is first.
		 */
		protected final boolean tryAcquire(int acquires) {
			final Thread current = Thread.currentThread();
			int c = getState();
			if (c == 0) {// 初始化状态
				if (!hasQueuedPredecessors() && compareAndSetState(0, acquires)) {
					setExclusiveOwnerThread(current);
					return true;
				}
			} else if (current == getExclusiveOwnerThread()) {// 重入
				int nextc = c + acquires;
				if (nextc < 0)
					throw new Error("Maximum lock count exceeded");
				setState(nextc);
				return true;
			}
			return false;
		}
	}

	/**
	 * Creates an instance of {@code ReentrantLock}. This is equivalent to using
	 * {@code ReentrantLock(false)}.
	 */
	public ReentrantLock() {
		sync = new NonfairSync();
	}

	/**
	 * Creates an instance of {@code ReentrantLock} with the given fairness
	 * policy.
	 *
	 * @param fair
	 *            {@code true} if this lock should use a fair ordering policy
	 */
	public ReentrantLock(boolean fair) {
		sync = fair ? new FairSync() : new NonfairSync();
	}

	/**
	 * Acquires the lock.
	 *
	 * <p>
	 * Acquires the lock if it is not held by another thread and returns
	 * immediately, setting the lock hold count to one.
	 *
	 * <p>
	 * If the current thread already holds the lock then the hold count is
	 * incremented by one and the method returns immediately.
	 *
	 * <p>
	 * If the lock is held by another thread then the current thread becomes
	 * disabled for thread scheduling purposes and lies dormant until the lock
	 * has been acquired, at which time the lock hold count is set to one.
	 */
	public void lock() {
		sync.lock();
	}

	/**
	 * Acquires the lock unless the current thread is
	 * {@linkplain Thread#interrupt interrupted}.
	 *
	 * <p>
	 * Acquires the lock if it is not held by another thread and returns
	 * immediately, setting the lock hold count to one.
	 *
	 * <p>
	 * If the current thread already holds this lock then the hold count is
	 * incremented by one and the method returns immediately.
	 *
	 * <p>
	 * If the lock is held by another thread then the current thread becomes
	 * disabled for thread scheduling purposes and lies dormant until one of two
	 * things happens:
	 *
	 * <ul>
	 *
	 * <li>The lock is acquired by the current thread; or
	 *
	 * <li>Some other thread {@linkplain Thread#interrupt interrupts} the
	 * current thread.
	 *
	 * </ul>
	 *
	 * <p>
	 * If the lock is acquired by the current thread then the lock hold count is
	 * set to one.
	 *
	 * <p>
	 * If the current thread:
	 *
	 * <ul>
	 *
	 * <li>has its interrupted status set on entry to this method; or
	 *
	 * <li>is {@linkplain Thread#interrupt interrupted} while acquiring the
	 * lock,
	 *
	 * </ul>
	 *
	 * then {@link InterruptedException} is thrown and the current thread's
	 * interrupted status is cleared.
	 *
	 * <p>
	 * In this implementation, as this method is an explicit interruption point,
	 * preference is given to responding to the interrupt over normal or
	 * reentrant acquisition of the lock.
	 *
	 * @throws InterruptedException
	 *             if the current thread is interrupted
	 */
	public void lockInterruptibly() throws InterruptedException {
		sync.acquireInterruptibly(1);
	}

	/**
	 * Acquires the lock only if it is not held by another thread at the time of
	 * invocation.
	 *
	 * <p>
	 * Acquires the lock if it is not held by another thread and returns
	 * immediately with the value {@code true}, setting the lock hold count to
	 * one. Even when this lock has been set to use a fair ordering policy, a
	 * call to {@code tryLock()} <em>will</em> immediately acquire the lock if
	 * it is available, whether or not other threads are currently waiting for
	 * the lock. This &quot;barging&quot; behavior can be useful in certain
	 * circumstances, even though it breaks fairness. If you want to honor the
	 * fairness setting for this lock, then use {@link #tryLock(long, TimeUnit)
	 * tryLock(0, TimeUnit.SECONDS) } which is almost equivalent (it also
	 * detects interruption).
	 *
	 * <p>
	 * If the current thread already holds this lock then the hold count is
	 * incremented by one and the method returns {@code true}.
	 *
	 * <p>
	 * If the lock is held by another thread then this method will return
	 * immediately with the value {@code false}.
	 *
	 * @return {@code true} if the lock was free and was acquired by the current
	 *         thread, or the lock was already held by the current thread; and
	 *         {@code false} otherwise
	 */
	public boolean tryLock() {
		return sync.nonfairTryAcquire(1);
	}

	/**
	 * Acquires the lock if it is not held by another thread within the given
	 * waiting time and the current thread has not been
	 * {@linkplain Thread#interrupt interrupted}.
	 *
	 * <p>
	 * Acquires the lock if it is not held by another thread and returns
	 * immediately with the value {@code true}, setting the lock hold count to
	 * one. If this lock has been set to use a fair ordering policy then an
	 * available lock <em>will not</em> be acquired if any other threads are
	 * waiting for the lock. This is in contrast to the {@link #tryLock()}
	 * method. If you want a timed {@code tryLock} that does permit barging on a
	 * fair lock then combine the timed and un-timed forms together:
	 *
	 * <pre>
	 * if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
	 * </pre>
	 *
	 * <p>
	 * If the current thread already holds this lock then the hold count is
	 * incremented by one and the method returns {@code true}.
	 *
	 * <p>
	 * If the lock is held by another thread then the current thread becomes
	 * disabled for thread scheduling purposes and lies dormant until one of
	 * three things happens:
	 *
	 * <ul>
	 *
	 * <li>The lock is acquired by the current thread; or
	 *
	 * <li>Some other thread {@linkplain Thread#interrupt interrupts} the
	 * current thread; or
	 *
	 * <li>The specified waiting time elapses
	 *
	 * </ul>
	 *
	 * <p>
	 * If the lock is acquired then the value {@code true} is returned and the
	 * lock hold count is set to one.
	 *
	 * <p>
	 * If the current thread:
	 *
	 * <ul>
	 *
	 * <li>has its interrupted status set on entry to this method; or
	 *
	 * <li>is {@linkplain Thread#interrupt interrupted} while acquiring the
	 * lock,
	 *
	 * </ul>
	 * then {@link InterruptedException} is thrown and the current thread's
	 * interrupted status is cleared.
	 *
	 * <p>
	 * If the specified waiting time elapses then the value {@code false} is
	 * returned. If the time is less than or equal to zero, the method will not
	 * wait at all.
	 *
	 * <p>
	 * In this implementation, as this method is an explicit interruption point,
	 * preference is given to responding to the interrupt over normal or
	 * reentrant acquisition of the lock, and over reporting the elapse of the
	 * waiting time.
	 *
	 * @param timeout
	 *            the time to wait for the lock
	 * @param unit
	 *            the time unit of the timeout argument
	 * @return {@code true} if the lock was free and was acquired by the current
	 *         thread, or the lock was already held by the current thread; and
	 *         {@code false} if the waiting time elapsed before the lock could
	 *         be acquired
	 * @throws InterruptedException
	 *             if the current thread is interrupted
	 * @throws NullPointerException
	 *             if the time unit is null
	 *
	 */
	public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
		return sync.tryAcquireNanos(1, unit.toNanos(timeout));
	}

	/**
	 * Attempts to release this lock.
	 *
	 * <p>
	 * If the current thread is the holder of this lock then the hold count is
	 * decremented. If the hold count is now zero then the lock is released. If
	 * the current thread is not the holder of this lock then
	 * {@link IllegalMonitorStateException} is thrown.
	 *
	 * @throws IllegalMonitorStateException
	 *             if the current thread does not hold this lock
	 */
	public void unlock() {
		sync.release(1);
	}

	/**
	 * Returns a {@link Condition} instance for use with this {@link Lock}
	 * instance.
	 *
	 * <p>
	 * The returned {@link Condition} instance supports the same usages as do
	 * the {@link Object} monitor methods ({@link Object#wait() wait},
	 * {@link Object#notify notify}, and {@link Object#notifyAll notifyAll})
	 * when used with the built-in monitor lock.
	 *
	 * <ul>
	 *
	 * <li>If this lock is not held when any of the {@link Condition}
	 * {@linkplain Condition#await() waiting} or {@linkplain Condition#signal
	 * signalling} methods are called, then an
	 * {@link IllegalMonitorStateException} is thrown.
	 *
	 * <li>When the condition {@linkplain Condition#await() waiting} methods are
	 * called the lock is released and, before they return, the lock is
	 * reacquired and the lock hold count restored to what it was when the
	 * method was called.
	 *
	 * <li>If a thread is {@linkplain Thread#interrupt interrupted} while
	 * waiting then the wait will terminate, an {@link InterruptedException}
	 * will be thrown, and the thread's interrupted status will be cleared.
	 *
	 * <li>Waiting threads are signalled in FIFO order.
	 *
	 * <li>The ordering of lock reacquisition for threads returning from waiting
	 * methods is the same as for threads initially acquiring the lock, which is
	 * in the default case not specified, but for <em>fair</em> locks favors
	 * those threads that have been waiting the longest.
	 *
	 * </ul>
	 *
	 * @return the Condition object
	 */
	public Condition newCondition() {
		return sync.newCondition();
	}

	/**
	 * Queries the number of holds on this lock by the current thread.
	 *
	 * <p>
	 * A thread has a hold on a lock for each lock action that is not matched by
	 * an unlock action.
	 *
	 * <p>
	 * The hold count information is typically only used for testing and
	 * debugging purposes. For example, if a certain section of code should not
	 * be entered with the lock already held then we can assert that fact:
	 *
	 * <pre>
	 * class X {
	 * 	ReentrantLock lock = new ReentrantLock();
	 * 
	 * 	// ...
	 * 	public void m() {
	 * 		assert lock.getHoldCount() == 0;
	 * 		lock.lock();
	 * 		try {
	 * 			// ... method body
	 * 		} finally {
	 * 			lock.unlock();
	 * 		}
	 * 	}
	 * }
	 * </pre>
	 *
	 * @return the number of holds on this lock by the current thread, or zero
	 *         if this lock is not held by the current thread
	 */
	public int getHoldCount() {
		return sync.getHoldCount();
	}

	/**
	 * Queries if this lock is held by the current thread.
	 *
	 * <p>
	 * Analogous to the {@link Thread#holdsLock} method for built-in monitor
	 * locks, this method is typically used for debugging and testing. For
	 * example, a method that should only be called while a lock is held can
	 * assert that this is the case:
	 *
	 * <pre>
	 * class X {
	 * 	ReentrantLock lock = new ReentrantLock();
	 * 
	 * 	// ...
	 * 
	 * 	public void m() {
	 * 		assert lock.isHeldByCurrentThread();
	 * 		// ... method body
	 * 	}
	 * }
	 * </pre>
	 *
	 * <p>
	 * It can also be used to ensure that a reentrant lock is used in a
	 * non-reentrant manner, for example:
	 *
	 * <pre>
	 * class X {
	 * 	ReentrantLock lock = new ReentrantLock();
	 * 
	 * 	// ...
	 * 
	 * 	public void m() {
	 * 		assert !lock.isHeldByCurrentThread();
	 * 		lock.lock();
	 * 		try {
	 * 			// ... method body
	 * 		} finally {
	 * 			lock.unlock();
	 * 		}
	 * 	}
	 * }
	 * </pre>
	 *
	 * @return {@code true} if current thread holds this lock and {@code false}
	 *         otherwise
	 */
	public boolean isHeldByCurrentThread() {
		return sync.isHeldExclusively();
	}

	/**
	 * Queries if this lock is held by any thread. This method is designed for
	 * use in monitoring of the system state, not for synchronization control.
	 *
	 * @return {@code true} if any thread holds this lock and {@code false}
	 *         otherwise
	 */
	public boolean isLocked() {
		return sync.isLocked();
	}

	/**
	 * Returns {@code true} if this lock has fairness set true.
	 *
	 * @return {@code true} if this lock has fairness set true
	 */
	public final boolean isFair() {
		return sync instanceof FairSync;
	}

	/**
	 * Returns the thread that currently owns this lock, or {@code null} if not
	 * owned. When this method is called by a thread that is not the owner, the
	 * return value reflects a best-effort approximation of current lock status.
	 * For example, the owner may be momentarily {@code null} even if there are
	 * threads trying to acquire the lock but have not yet done so. This method
	 * is designed to facilitate construction of subclasses that provide more
	 * extensive lock monitoring facilities.
	 *
	 * @return the owner, or {@code null} if not owned
	 */
	protected Thread getOwner() {
		return sync.getOwner();
	}

	/**
	 * Queries whether any threads are waiting to acquire this lock. Note that
	 * because cancellations may occur at any time, a {@code true} return does
	 * not guarantee that any other thread will ever acquire this lock. This
	 * method is designed primarily for use in monitoring of the system state.
	 *
	 * @return {@code true} if there may be other threads waiting to acquire the
	 *         lock
	 */
	public final boolean hasQueuedThreads() {
		return sync.hasQueuedThreads();
	}

	/**
	 * Queries whether the given thread is waiting to acquire this lock. Note
	 * that because cancellations may occur at any time, a {@code true} return
	 * does not guarantee that this thread will ever acquire this lock. This
	 * method is designed primarily for use in monitoring of the system state.
	 *
	 * @param thread
	 *            the thread
	 * @return {@code true} if the given thread is queued waiting for this lock
	 * @throws NullPointerException
	 *             if the thread is null
	 */
	public final boolean hasQueuedThread(Thread thread) {
		return sync.isQueued(thread);
	}

	/**
	 * Returns an estimate of the number of threads waiting to acquire this
	 * lock. The value is only an estimate because the number of threads may
	 * change dynamically while this method traverses internal data structures.
	 * This method is designed for use in monitoring of the system state, not
	 * for synchronization control.
	 *
	 * @return the estimated number of threads waiting for this lock
	 */
	public final int getQueueLength() {
		return sync.getQueueLength();
	}

	/**
	 * Returns a collection containing threads that may be waiting to acquire
	 * this lock. Because the actual set of threads may change dynamically while
	 * constructing this result, the returned collection is only a best-effort
	 * estimate. The elements of the returned collection are in no particular
	 * order. This method is designed to facilitate construction of subclasses
	 * that provide more extensive monitoring facilities.
	 *
	 * @return the collection of threads
	 */
	protected Collection<Thread> getQueuedThreads() {
		return sync.getQueuedThreads();
	}

	/**
	 * Queries whether any threads are waiting on the given condition associated
	 * with this lock. Note that because timeouts and interrupts may occur at
	 * any time, a {@code true} return does not guarantee that a future
	 * {@code signal} will awaken any threads. This method is designed primarily
	 * for use in monitoring of the system state.
	 *
	 * @param condition
	 *            the condition
	 * @return {@code true} if there are any waiting threads
	 * @throws IllegalMonitorStateException
	 *             if this lock is not held
	 * @throws IllegalArgumentException
	 *             if the given condition is not associated with this lock
	 * @throws NullPointerException
	 *             if the condition is null
	 */
	public boolean hasWaiters(Condition condition) {
		if (condition == null)
			throw new NullPointerException();
		if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
			throw new IllegalArgumentException("not owner");
		return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject) condition);
	}

	/**
	 * Returns an estimate of the number of threads waiting on the given
	 * condition associated with this lock. Note that because timeouts and
	 * interrupts may occur at any time, the estimate serves only as an upper
	 * bound on the actual number of waiters. This method is designed for use in
	 * monitoring of the system state, not for synchronization control.
	 *
	 * @param condition
	 *            the condition
	 * @return the estimated number of waiting threads
	 * @throws IllegalMonitorStateException
	 *             if this lock is not held
	 * @throws IllegalArgumentException
	 *             if the given condition is not associated with this lock
	 * @throws NullPointerException
	 *             if the condition is null
	 */
	public int getWaitQueueLength(Condition condition) {
		if (condition == null)
			throw new NullPointerException();
		if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
			throw new IllegalArgumentException("not owner");
		return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject) condition);
	}

	/**
	 * Returns a collection containing those threads that may be waiting on the
	 * given condition associated with this lock. Because the actual set of
	 * threads may change dynamically while constructing this result, the
	 * returned collection is only a best-effort estimate. The elements of the
	 * returned collection are in no particular order. This method is designed
	 * to facilitate construction of subclasses that provide more extensive
	 * condition monitoring facilities.
	 *
	 * @param condition
	 *            the condition
	 * @return the collection of threads
	 * @throws IllegalMonitorStateException
	 *             if this lock is not held
	 * @throws IllegalArgumentException
	 *             if the given condition is not associated with this lock
	 * @throws NullPointerException
	 *             if the condition is null
	 */
	protected Collection<Thread> getWaitingThreads(Condition condition) {
		if (condition == null)
			throw new NullPointerException();
		if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
			throw new IllegalArgumentException("not owner");
		return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject) condition);
	}

	/**
	 * Returns a string identifying this lock, as well as its lock state. The
	 * state, in brackets, includes either the String {@code "Unlocked"} or the
	 * String {@code "Locked by"} followed by the {@linkplain Thread#getName
	 * name} of the owning thread.
	 *
	 * @return a string identifying this lock, as well as its lock state
	 */
	public String toString() {
		Thread o = sync.getOwner();
		return super.toString() + ((o == null) ? "[Unlocked]" : "[Locked by thread " + o.getName() + "]");
	}
}
